When it rains my toilet will act as if it is going to overflow when flushed. It goes down slowly. I live in the city and the main sewer line is in my front yard. My line connect to the main from my back yard. I've called the city out several times and they keep telling me this is normal during heavy rains. Well I think not. No one else is having this problem but me. I've called out a plumber to make sure it's not my pipe that is cracked or any other problem. There is nothing wrong. Please help!!!
Assuming the plumber has done a video inspection of your sewer line and not found any problems, if it only occurs when it rains, it would imply that you are either experiencing a backup from the city, or are close to having one. This is not that uncommon in large rainstorms, especially in areas where there is a single storm sewer and waste sewer. Newer areas might two separate sewer systems so this doesn't occur, but otherwise, all that rain is trying to enter the same sewer as your households waste system.
If you haven't had a video inspection, that should be your first step. There's no other way to definitively know about an issue like roots or a collapse in your sewer line.
The next t thing I would be checking is to ensure you're not actually experiencing a backup. A backup will occur in the lowest drain in your house - often a floor drain in the basement, or perhaps a basement bathtub or toilet.
Do you know if you have a backflow valve? If so, you should visually inspect this to ensure it is not closed. It will automatically close if the city is backing up. This prevents all of the cities sewage from entering your house, but it also prevents your waste from existing your house and it will instead build up in your pipes until it backs up. If you don't have a backflow valve, I would suggest you put one of these in urgently. The cost of the valve will be small compared to dealing with 4' of sewage water in your basement.
No guarantees, but this has a good chance of working.
The following sounds a bit exciting - it is. If you are able to deal with potentially dangerous stuff that is OK enough if used sensibly this may work for you. If not, get somebody else to try, or pay an expert.
It seems likely that you waste pipe is clogged either by paper and "misc other stuff" or by tree roots or similar that have entered the pipe. You don't say what the plumber or others did to check for problems but if they did not run a cleaning device down it or check it in some manner then there is no certainty that it is clear. So ...
Obtain say 500 grams / one pound of caustic soda flakes or strong caustic soda solution. This may be sold as Drain-O or perhaps lye or other names depending where you are. The chemical name is Sodium Hydroxide = NaOH. While much less than the amount above MAY work, this much does no harm and has best chance of working.
Dissolve flakes or add solution to about on large bucket of water. This is nasty stuff - as you'd hope. Do NOT use an aluminum container. Wear old clothes. Wear eye protection. Consider wearing rubber gloves. You can " safely enough" dip your hands in a full strength solution as long as you wash it off immediately. I do not suggest you ever do that (but I have) but it helps to add perspective. It's "safe enough" if you are sensible. Solution may get hot while being made. If it all will not dissolves in amount of water used, use just enough more water to dissolve it.
When ready, pour the lot steadily into toilet. Maybe pour a little more water after it but minimise water flow for a day or so. The aim is to get concentrated solution "down there". This will make toilet paper and associated nasties water soluble and will clear many blockages. It will work on tree roots but takes longer and main effect short term is probably to remove paper tangled on roots.
If it works for days to weeks then starts to get bad again, try adding a smaller does occasionally, to deal with stubborn obstructions over time.
Exciting answer from Russell McMahon, but I can't help thinking its either the city or major obstructions in your run to the sewer that's the problem.
Have you done a thorough survey of all your neighbors? If you see a trend, that might move the city to action.
And if its not the city, its your plumbing. Did your plumber actually scope the line? That info would help you move forward.
The city will check the connection between the main and the sewer line going to your house. If they came out a couple of times it's probably OK, because otherwise they would have cleaned it. If you are there when they are checking, you can try giving them some money to clean the portion of the sewer line that goes into your house. The other option is to call a plummer and have them run a camera to inspect your sewer. Finally, it could be just storm water backing up in your sewer line like the city says. If your sewer line is fine and the connection to the main sewer is fine, than it's probably that.